Television amplifier



Dec. 27, 193s.- K. SCHLAESINGER I TELEVISION AMPLIFIER Filed Dec. 17, 1934 I Jnrenior:

Patented Dec. 27, 1938 PA'i'ET owner.

TELEVISION AMPLIFIER "Kurt Schlesinger, Berlin, Germany, assignor to Radioaktiengesellschaft D. S. Loewe, Berlin- Steglitz, Germany Application December 17, 1934, Serial No. 757,773 In Germany December 20,1933

3 Claims.

The invention relates to the problem of the effective amplification of a wide frequency band, such as occurs in the case of television lowfrequency amplification or television intermediate frequency amplification. It is known that for these purposes comparatively low-ohmic anode resistances require to be employed, (for example, Ra=5000 ohms and less for images of approximately 50,000 image points and more). l0 The amplification per tube (constituted by the equation V=S.Ra) may, therefore, only be increased by the use of tubes with improved steepness S.

The subject matter of the invention is the introduction of an aperiodic reaction coupling, for example a feed-back or reflex connection with the aid of galvanic coupling of a feed-backcondenser, over every two tubes, and more particularly the use of a connection system of this nature specifically for television purposes The invention is described in conjunction with the appended drawing which shows diagrammatically an exemplary embodiment of the invention. There are shown in the drawing two tubes of an intermediate carrier-Wave amplifier.

The tubes form part of a superheterodyne receiver, which picks up the transmission on an ultra-short wave ('7 metres), then passes the same by means of a connection system known per se to an intermediate wave of approximately 150 metres, and after amplification rectifies this intermediate wave. The said intermediate wave is surrounded by side bands up to the extreme wave of 100 and 300 metres. This frequency band requires to be amplified as evenly and effectively as possible. An amplifier of ordinary construction should possess for this purpose not more than 4000 ohms as anode resistance I, whilst for avoiding of the undesired amplification of waves longer than the intermediate waves, the grid resistance 2 should be a comparatively low resistance, for example 10,000 ohms, and the condenser 3 should be approximately 5.5- mF. The amplification thus capable of being obtained is in the case of ordinary tubes with a working steepness of 2-3 milliamperes per volt merely approximately 8-12 per stage. In order to have an improvement in the amplification there is used a reaction circuit arrangement in combination with an impedance producing a defined resonance circuit arrangement in the anode circuit of that tube from which reaction is derived.

This impedance which is used additionally in accordance with the invention, consists of a coil I (see drawing), which produces with its selfcapacity 3 indicated in broken lines a defined resonance effect. This coil 7- which may be damped as desired by means of a parallel resistance 9 is connected between the anode resistance of the valve from which reaction is derived and the positive terminal of the anode supply source, the negative terminal of which is earthed.

The feed-back connection is performed by a variable condenser H which is lying in the line l0 connecting the grid of the preceding valve with the connection point of the anode resistance 5 and the parallel connection network 1, 8, 9. By means of this resonant circuit arrangement a preferred reaction coupling of those frequency bands which are selective as desired may be effectedand correspondingly by adjusting a defined resonance effect an improvement in the amplific'ation of the whole circuit arrangement is effected. The variable condenser H is chosen to have a maximum capacity of 5.5-10 F. The amplification is then improved only in respect of frequencies in the vicinity of the natural frequency of the structure I, 8, 9. Low frequencies, in very desirable fashion, are afiected adversely as compared with these higher frequencies. This effect is very desirable in the case of carrierwave amplification, as the same offers the advantage of reduced liability to interference in comparison with simple full aperiodic resistance amplifiers.

Naturally in place of the stated coupling im-" pedances l, 8 it is also possible to employ as desired other coupling impedances composed of resistances, condensers and coils for backcoupling purposes, and accordingly a desired improvement in the amplification may be adjusted in respect of a frequency band selected as desired. The optimum frequency of the resistance amplifier to which the reflection isto be applied is disposed to coincide with the natural frequency of said impedance. The resistance amplifier per se amplifies without distortion only in respect of that frequency which is best amplified, i. e. for which the amplifier is dimensioned so that back-couplings may be readily produced only for the range of this frequency, and on the other hand even weak reaction couplings are sufficient for obtaining large improvements, so that the danger of self-excitation in this coincidence of the natural frequency curve with the frequency curve of the feed-back coupling according to the invention is reduced to a minimum.

The coupling may also be taken more particularly whilst omitting intermediate stages over the first and fourth stages, or when employing semiaperiodic transformer couplings as described for example in detail in the application Ser. No. 749,511 over an odd number of stages, as the transformer coupling permits of phase-reversal by simple change of polarity and thus dispenses with the intermediate tube.

I claim:

1. In a television amplifier system a regenera tive intermediate carrier frequency amplifier, included in a super-heterodyne receiver, for amplifying wide television frequency bands, comprising a plurality of amplifier stages, coupled with each other by resistance capacity coupling means, means in said amplifier forming a feedback connection between said'amplifier stages in aperiodic fashion, i. e., aperiodic for said large frequency band to be amplified, said feed-back connection means consisting of a variable condenser in combination with an impedance producing a defined resonance effect with its selfcapacity and being damped by a parallel resistance, said means being dependent on the frequency to be amplified.

2. In a television amplifier system a regenerative intermediate carrier frequency amplifier, included in a super-heterodyne receiver, for amplifying wide television frequency bands, comprising a plurality of amplifier stages, coupled with each other by resistance capacity coupling means, means in said amplifierforming a feedback connection between said amplifier stages in galvanic aperiodic fashion, 1. e., aperiodic for said large frequency band to be amplified, said'feedback connection means consisting of a selfinduction in the anode circuit of an amplifier valve, a damping resistance connected in parallel to said self-induction, said parallel connection net-work being connected between the anode resistance of said valve and the positive terminal of the anode supply source, the negative terminal of which is earthed, and a variable condenser, the one electrode of said condenser being connected between'the connection point of said anode resistance and said parallel connection net-work, and the other electrode of said condenser being connected to the grid of the preceding valve.

3 In a television amplifier system a regenerative intermediate carrier frequency amplifier, included'in a 'super-heterodyne receiver, for amplifying wide televisionfrequency bands, comprising a plurality of amplifier stages, coupled with each other by resistance capacity coupling means, means in said amplifier forming a feedback connection between said amplifier stages in galvanic aperiodic fashion, i. e., aperiodic for said large frequency band to be amplified, said feed-back connection means consisting of a selfinduction in the anode circuit of an amplifier valve, a damping resistance connected in parallel to said self-induction, said parallel connection net-work being connected between the anode resistance of said valve and the positive terminal of the anode supply source, the negative termi: nal of which is earthed, and a variable condenser, the one electrode of said condenser being connected between the connection point of said anode resistance and said parallel connection network, and the other electrode of said condenser being connected to the grid of the preceding valve, the natural frequency of said self induction coinciding with the optimum frequency amplified by said amplifier without phase distortion.

. KURT SCHLESINGER. 

